Apparatus for supplying power and liquid crystal display having the same

ABSTRACT

Disclosed are a power supplying apparatus and a LCD having the same that reduces manufacturing cost of a large-scale LCD module and enhances powpower efficiency by integrating an external dc power supply used in a large-scale LCD panel into a LCD panel. A first voltage converter converts an external ac voltage into a first dc voltage, and changes a voltage level of the first de voltage into a second dc voltage having a highr voltage level than that of the first de voltage. A second voltage converter converts the second dc voltage into an ac voltage, raises a voltage level of the converted ac voltage, and provides the raised ac voltage to a load. A current detector detects a current flowing through the load, and provides a current detection signal as a feedback signal to the first voltage converter so that the first voltage provide a constant direct current output voltage.

TECHNICAL FIELD

The present invention relates to a liquid crystal display (LCD), andmore particularly to a power supplying apparatus and a LCD having thesame that reduces cost for manufacturing a large-scale LCD module andenhances power efficiency.

BACKGROUND ART

A LCD monitor is usually used in a notebook computer, the LCD monitorused in the notebook computer should be supplied with a power from abattery or an external dc (direct current) power supply due tocharacteristics of the notebook computer.

FIG. 1 is a block diagram illustrating a conventional LCD monitor usedin a desktop computer.

Referring to FIG. 1, the conventional LCD monitor used in the desktopcomputer includes a power input section 10 and a LCD module 20. Thepower input section 10 includes an AC input section 12, an ac-to-dcrectifier 14 and a dc-to-dc converter 16. The LCD module 20 includes adc-to-ac inverter 22, a backlight unit 23, a dc-to-dc converter 24 and aLCD panel section 25.

However, as shown in FIG. 1, an external dc power supply—i.e. anadaptor—is still used for the LCD monitor of the desktop computer. Anexterior of the LCD monitor used in the desktop computer does not lookneat because an external power supply is equipped with the LCD monitorby connecting the external dc power supply to the LCD monitor of thedesktop computer.

In addition, a power is supplied from the external power supply, andthen the power is converted into a power having a different power levelappropriate for the LCD module, so that the power efficiency is reduced.

DISCLOSURE OF THE INVENTION

The present invention provides an adapter-free power supply having abuilt in dc power supply.

The present invention also provides a LCD that reduces cost formanufacturing the LCD and enhances power efficiency by integrating theexternal dc power supply into the LCD panel.

The present invention also provides a LCD that equipped with theadapter-free power supply having a built in dc power supply.

In one aspect of the invention, there is provided a power supplyingapparatus, comprising: a first voltage converting means for converting afirst alternating current voltage into a first direct current voltage,and for changing a voltage level of the first direct current voltageinto a second direct current voltage having a higher voltage level thanthe voltage level of the first direct current voltage; a second voltageconverting means for converting the second direct current voltage into asecond alternating current voltage, and for changing a voltage level ofthe second alternating current voltage into a third alternating currentvoltage having a higher voltage level than the voltage level of thesecond alternating current voltage to provide the third alternatingcurrent voltage to a first load; and a current detector for detecting acurrent flowing through the first load, and for providing a currentdetecting signal to the first voltage converting means so that the firstvoltage converting means provide a constant direct current outputvoltage.

Preferably, the first voltage converting means comprises: a rectifyingmeans for rectifying the first alternating current voltage into thefirst direct current voltage; and a dc-to-dc converter for convertingthe first direct current voltage into the second direct current voltageto provide the second direct current voltage to the second voltageconverting means, and wherein the dc-to-dc converter varies the voltagelevel of the second direct current voltage in response to the detectedcurrent signal.

Preferably, the second voltage converting means is a royer inverter, andthe second voltage converting means comprises: a transformer including aprimary coil and a secondary coil, the primary coil of the transformerbeing connected to an output terminal of the first voltage convertingmeans, and the secondary coil of the transformer being connected thefirst load; a resonance capacitor, being connected parallel with theprimary coil, to form a LC resonance circuit; a first transistor, a baseof the first transistor being connected to the output terminal of thefirst voltage converting means, a collector of the first transistorbeing connected to a first end of the resonance capacitor, and anemitter of the first transistor being connected to a ground, for drivingthe transformer; a second transistor, a base of the second transistorbeing connected to the output terminal of the first voltage convertingmeans, a collector of the second transistor being connected to a secondend of the resonance capacitor, and an emitter of the second transistorbeing connected to the ground, for driving the transformer.

In addition, preferably, the first voltage converting means furthergenerates a third directing current voltage having a voltage level lowerthan the voltage level of the first direct current voltage and providesthe third direct current voltage to a second load, by receiving thefirst alternating current voltage. The power supplying apparatus furthercomprises a third voltage converting means for providing the thirddirect current voltage to the second load.

In another aspect of the invention, there is provided a LCD apparatus,comprising: a LCD panel driving means for generating a driving signal; aLCD panel for displaying an image based on the driving signal from theLCD panel driving means; a backlight unit, disposed under the LCD panel,for providing a light to the LCD panel; a first voltage converting meansfor converting a first alternating current voltage into a first directcurrent voltage; a second voltage converting means for converting thefirst direct current voltage into a second alternating current voltageto provide the second alternating current voltage to the backlight unit;and a third voltage converting means for converting the first directcurrent voltage into a second directing current voltage to provide thesecond directing current voltage to the LCD panel driving means.

Preferably, the first voltage converting means performs a power factorcorrection function when converting the first alternating currentvoltage into the first direct current voltage.

In addition, preferably, the first voltage converting means comprises adiode rectifier circuit or an active PWM rectifier circuit.

Preferably, the second voltage converting means comprises one selectedfrom the group consisting of a buck converter, a boost converter, ahalf-bridge converter, a flyback converter, a push-pull converter and aforward converter. In addition, preferably, the third voltage convertingmeans comprises one selected from the group consisting of a royerInverter, a push-pull Inverter, a half bridge Inverter and a full-bridgeInverter.

In further another aspect of the invention, there is provided a LCDapparatus, comprising: a LCD panel for displaying an image based on adriving signal from a plurality of LCD panel drivers; a backlight unit,disposed under the LCD panel, for providing a light to the LCD panel; afirst voltage converting means for converting a first alternatingcurrent voltage into a first direct current voltage, and for changing avoltage level of the first direct current voltage into a second directcurrent voltage having a higher voltage level than the voltage level ofthe first direct current voltage in respond to a voltage raising-controlsignal; a second voltage converting means for converting the seconddirect current voltage into a second alternating current voltage, andfor changing a voltage level of the second alternating current voltageinto a third alternating current voltage having a higher voltage levelthan the voltage level of the second alternating current voltage toprovide the third alternating current voltage to the backlight unit; acurrent detector for detecting a current flowing through the backlight,and for providing the voltage raising-control signal to the firstvoltage converting means; and a third voltage converting means forconverting the second directing current voltage into a plurality ofthird directing current voltage to provide the third direct currentvoltage to each of the LCD panel driver.

According to the present invention, the power supplying apparatus andthe LCD having the same can provides a high voltage to the fluorescentlamp by a simple circuit, reduces manufacturing cost of a large-scaleLCD module, and enhances power efficiency by integrating an external dcpower supply used in a large-scale LCD panel into a LCD panel.

BRIEF DESCRIPTION OF DRAWINGS

The above and other advantages of the present invention will becomereadily apparent by describing an exemplary embodiment with reference tothe accompanying drawings in which:

FIG. 1 is a block diagram illustrating a LCD monitor used inconventional desktop computer;

FIG. 2 is a block diagram illustrating a LCD according to one exemplaryembodiment of the present invention;

FIG. 3 is a circuit diagram showing a first specific circuit forimplementing the LCD in FIG. 2;

FIG. 4 is a circuit diagram showing a second specific circuit forimplementing the LCD in FIG. 2;

FIG. 5 is a block diagram illustrating a power supplier according to oneexemplary embodiment of the present invention;

FIG. 6 is a block diagram illustrating a LCD having the power supply inFIG. 5 according to one exemplary embodiment of the present invention;and

FIG. 7 is a circuit diagram showing a specific circuit for implementingthe power supplier in FIG. 6.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 2 is a block diagram illustrating a LCD according to one exemplaryembodiment of the present invention;

Referring to FIG. 2, the LCD includes an AC (alternating current) inputsection 100 and a LCD module 200.

The AC input section 100 receives a general alternating current voltagehaving a current level between about 100 volts and about 240 volts andprovides the general alternating current voltage to the LCD module 200.Generally, the LCD module 200 can be provided with the generalalternating current voltage by putting an electric plug into aplug-socket.

The LCD module 200 includes an ac-to-dc rectifier 210, a dc-to-acinverter 220, a backlight unit 230, a dc-to-dc voltage convertingsection 240 and a LCD panel 250. The LCD module 200 receives the generalalternating current voltage and displays an image provided from externalgraphic controller (not shown).

Specifically, the AC-to-DC rectifier 210 performs a power factorcorrection function when converting the general alternating currentvoltage in range of 100-240 volts into a high direct current voltage,and provides the converted direct current voltage to both the dc-to-dcvoltage converting section 240 and the dc-to-ac inverter 220.

The ac-to-dc rectifier 210 can be embodied by a diode rectifier or anactive pulse-width modulated (PWM) rectifier.

The dc-to-ac inverter 220 converts the high voltage generated from theac-to-dc rectifier 210, for example a high direct current voltage havinga voltage level between about 500 volts and 600 volts, into analternating current voltage 221 appropriate for the backlight unit andoutputs the alternating current voltage 221. The dc-to-ac inverter 220can be embodied by any kind of inverter driven under a high voltagehaving a voltage level between 500 volts and 600 volts except theinverter driven under a low voltage having a voltage level between 5volts and 12 volts. For example, the dc-to-ac inverter 220 can beembodied by a royer Inverter, a push-pull Inverter, a half bridgeInverter or a full-bridge Inverter.

Because the LCD module section 200 adopts the dc-to-ac inverter 220 thatconverts a high direct current voltage into a alternating currentvoltage, the LCD according to the present invention can use a moreeffective transformer with smaller coil turns in comparison with theconventional LCD monitor having a transformer with a large coil turns.Further, the LCD module section 200 can use the dc-to-ac inverter 220without a transformer, to thereby reduce the cost of manufacturing a LCDmonitor.

The backlight unit 230 includes fluorescent lamps disposed below abottom surface of a LCD panel 250, controls an optical power of thelight outputted from the fluorescent lamp based on the alternatingcurrent voltage 221 provided from the dc-to-ac inverter 220, and providethe light having a controlled optical power to the bottom surface of theLCD panel 250.

The dc-to-dc voltage converting section 240 includes a dc-to-dcconverter 242, a common-electrode voltage generator 244 and a gammavoltage generator 246, changes a dc voltage level of a high voltage, forexample in a range between 500 volts and 600 volts, into a low dcvoltage for driving a data driver, a scan driver or a LCD panel 250 ofthe LCD panel section 250.

Specifically, dc-to-dc voltage converting section 240 changes ahigh-level de voltage into a low level dc voltage, and provide the levelshifted de voltage to the common-electrode voltage generator 244 and thegamma voltage generator 246.

The dc-to-dc voltage converter 242 is embodied by a boost converter, abuck converter, a half-bridge converter, a flyback converter, afull-bridge converter, a push-pull converter and a forward converter.

The common-electrode voltage generator 244 generates a common-electrodevoltage (VCOM) based on the level shifted dc voltage from the dc-to-dcconverter 242, and provide the common-electrode voltage to the LCD panelsection 250. It is desirous that the level shifted dc voltage is a powersource for the common-electrode voltage generator 244.

The gamma voltage generator 246 generates a gamma voltage(VDD) based onthe level shifted dc voltage from the dc-to-dc converter 242, andprovides the gamma voltage to the LCD panel section 250. It is desirousthat the level shifted dc voltage is a gamma reference voltage.

The common-electrode voltage generator 244 and gamma voltage generator246 are included in the dc-to-dc voltage converting section 240includes, but it is also possible that the common-electrode voltagegenerator 244 and gamma voltage generator 246 are included in the LCDpanel section 250.

According to one preferred embodiment of the present invention, anexternal dc power supply, which is used in the conventional LCD monitorfor note book PC (Personal Computer), is directly installed inside theLCD module section 200 as a part of the LCD module section 200 insteadof directly connecting the external dc power supply with a LCD monitorfor a desk top PC, to thereby reduce the cost for manufacturing the LCDmonitor for a desk top PC.

In addition, according to one preferred embodiment of the presentinvention, the number of voltage converting steps decreases incomparison with that of the conventional voltage converting means.

FIG. 3 is a circuit diagram showing a first specific circuit forimplementing the LCD in FIG. 2.

Referring FIG. 2 and FIG. 3, the AC input section 100 provides thegeneral voltage having the voltage level between about 100 volts andabout 240 volts to the ac-to-dc rectifier 210.

The ac-to-dc rectifier 210 includes two parallel connected diode series(D1, D2, D3 and D4), receives the general voltage, rectifies the generalvoltage, and provides the rectified general voltage to the dc-to-dcvoltage converter 242-a.

The dc-to-dc converter 242-a is a boost converter that has a function ofa power factor correction (PFC). Specifically, the dc-to-dc converter242-a includes an inductor (L), a first MOSFET (Q1) and a capacitor (C).A first end of the inductor is connected a first end of the ac-to-dcdiode rectifier. A drain of the Q1 is connected to a second end of theinductor (L), the drain and source of the Q1 is connected parallel withthe diodes (D1, D2, D3, D4) through the inductor (L), and the source ofthe Q1 is connected to a second end of the ac-to-dc rectifier 210. Afirst end of the capacitor (C) is connected to an anode of a diode (D5)and a second end of the capacitor (C) is connected to the source of theQ1. The dc-to-dc converter 242-a raises the rectified voltage providedfrom the ac-to-dc rectifier 210, and provides the raised voltage to thedc-to-ac inverter 220 and a second dc-to-dc converter 242-b.

The dc-to-ac inverter 220 includes four MOSFETs (Q2, Q3, Q4 and Q5), adrain and a source of each MOSFET being connected with a diode, and afirst transformer (T1). The dc-to-ac inverter 220 outputs a voltage fora backlight of a CCFL (Cold Cathode Fluorescent Lamp).

Specifically, the Q2 is connected with a diode through the drain andsource of the Q2. The drain of the Q3 is connected serially to thesource of the Q2, the source of the Q3 is connected a second end of thecapacitor (C), and the drain and source of the Q3 is connected parallelwith a diode. The drain of the Q4 is connected to the drain of the Q2,the drain and source of the Q4 is connected parallel with a diode. Thedrain of the Q5 is connected serially to the source of the Q4, thesource of the Q5 is connected the source of the Q3, and the drain andsource of the Q5 is connected parallel with a diode. A first end of theprimary coil of T1 is connected with a common terminal between the Q2and Q3, and a second end of the primary coil is connected with commonterminal between the Q4 and Q5. The secondary coil of T1 is connected toa fluorescent lamp, raises a dc voltage inputted from the primary coilbase on winding number of T1, and provides the raised voltage to thefluorescent lamp.

The second dc-to-dc converter 242-b is a flyback converter having amultiple output function, receives the raised voltage from the firstdc-to-dc converter 242-a, and outputs a plurality of output voltages.

Especially, the second dc-to-dc converter 242-b includes a sixth MOSFET(Q6) which is connected to a diode through a drain and source of the Q6,a primary coil of T2 for generating a main power source, a magneticcore, a plurality of secondary coil of T2 for generating a plurality ofsubsidiary power source. The second dc-to-dc converter 242-b transmits adc voltage inputted from the primary coil of T2 to the plurality ofsecondary coil of T2 through the magnetic core.

Preferably, the output voltage outputted through the primary coil of T2can be used as a power source for the data driver that consumes a lot ofpower. The output voltage outputted through the secondary coil can beapplied to the scan driver, and can be used as a gate on/off voltage(Von/Voff) for controlling turn-on or turn-off, as a reference voltageof the common-electrode voltage (Vcom) that is applied to acommon-electrode line, and as a reference voltage for generating a gammavoltage.

FIG. 4 is a circuit diagram showing a second specific circuit forimplementing the LCD in FIG. 2.

Referring to FIG. 2 and FIG. 4, the AC input section 100 provides thegeneral ac voltage having the voltage level between about 100 volts andabout 240 volts to the ac-to-dc rectifier 210.

The ac-to-dc rectifier 210 includes a bridge diode that converts thegeneral ac voltage into a dc voltage, an inductor. (L), a first MOSFET(Q1) that is connected parallel to the bridge diode through the inductor(L), a fifth diode (D5) and a capacitor (C). The ac-to-dc rectifier 210includes a dc-to-dc converter, receives the general ac voltage,rectifies the general ac voltage into a dc voltage, and provides therectified general voltage to the dc-to-ac inverter 220 and dc-to-dcvoltage converter 242.

The bridge diode includes diodes (D1, D2, D3 and D4), rectifies thegeneral ac voltage through the serially connected first and second diode(D1, D2) and third and fourth diodes (D3, D4), and changes a dc voltagelevel of the rectified general voltage through the dc-to-dc converterthat includes a inductor (L), a first MOSFET (Q1) connected parallel tothe bridge diode through the inductor (L), a fifth diode (D5) and acapacitor (C), and provides the level shifted dc voltage to the dc-to-acinverter 220 and dc-to-dc voltage converter 242.

Especially, the ac-to-dc rectifier 210 includes a boost dc-to-dcconverter that has a function of a power factor correction (PFC).Specifically, the boost dc-to-dc converter includes an inductor (L), afirst MOSFET (Q1) and a capacitor (C). A first end of the inductor isconnected a first end of the bridge diode. A drain and source of the Q1is connected parallel with the bridge diodes through the inductor (L),the drain of the Q1 is connected to a second end of the inductor (L),and the source of the Q1 is connected to a second end of the bridgediode. A first end of the capacitor (C) is connected to an anode of adiode (D5) and a second end of the capacitor (C) is connected to thesource of the Q1. The boost dc-to-dc converter raises the rectifiedvoltage provided from the bridge diode in response to a control signalinputted from a gate of the Q1, and provides the raised voltage to thedc-to-ac inverter 220 and a dc-to-dc converter 242. The control signalapplied to the gate of the Q1 is a detecting signal that is generated inresponse to a lamp tube current flowing through a fluorescent lamp. Thecontrol signal controls the raised voltage level of the boost dc-to-dcconverter when detecting over-current through the fluorescent lamp.

The dc-to-ac inverter 220 includes four MOSFETs (Q2, Q3, Q4 and Q5), adrain and a source of each MOSFET being connected with a diode, and afirst transformer (T1). The dc-to-ac inverter 220 outputs a voltage fora backlight.

The dc-to-dc converter 242 is a flyback converter having a multipleoutput function, receives the raised voltage from the ac-to-dc rectifier210, and outputs a plurality of output voltages. A detail explanationabout the dc-to-ac inverter 220 will not be repeated here because thedetail description about the dc-to-ac inverter 220 is already given inFIG. 3.

On the other hand, a light source for replacing the conventional CCFLlamp has been developed as a light source of a backlight used in a LCDTV. A surface light source of a fluorescent lamp type, for example, candrives the entire LCD panel by only one driving circuit, can provide alight having a more uniform brightness to the entire LCD panel than theCCFL lamp for driving the direct type backlight. As a result, thethickness of the LCD panel can be maintained thin.

However, a operation voltage increases to a voltage level more than 2.5Kv, especially more than 3.0 Kv in proportion to an increased length ofthe lamp tube because a fluorescent lamp should be bent so as to coverthe entire surface of the LCD panel. The operation voltage of thesurface light source of a fluorescent lamp type is higher than theoperation voltage of the conventional CCFL, which is about 600-800volts, by about 2.5-5 times. Accordingly, it is difficult to drive thesurface light source of a fluorescent lamp type.

In addition, an EEFL (External Electrode Fluorescent Lamp) that hasexternal electrodes on both ends of the fluorescent lamp tube, or EIFL(External Internal electrode Fluorescent Lamp) that has an external andinternal electrode on a first and second end of the fluorescent lamptube, respectively, has been developed. However, these EEFL or EIFL alsorequires a higher operation voltage than the conventional CCFL.

Hereinafter, a power supply for a fluorescent lamp that requires a highoperation voltage is disclosed.

FIG. 5 is a block diagram illustrating a power supplier, especially forsupplying a voltage to a load consuming a high voltage, according to oneexemplary embodiment of the present invention,

Referring to FIG. 5, the power supply of the present invention includesan AC input section 100, a first voltage converting section 300, asecond voltage converting section 400 and a current detecting section600.

The AC input section 100 provides a general voltage having a voltagelevel between 100 volts and 240 volts to the first voltage convertingsection 300.

The first voltage converting section 300 is an adaptor that includes arectifier 310 and a dc-to-dc converter 320. The first voltage convertingsection 300 rectifiers the general ac voltage signal 101, converts therectified signal into a dc voltage signal 321, provides the converted dcvoltage signal 321 to the second voltage converting section 400, andcontrols a voltage level of the dc voltage signal that is outputted tothe second voltage converting section 400 in response to a currentdetecting signal 601 provided from the current detecting section 600.

Specifically, the rectifier 310 rectifies the general ac voltage signal101 provided from the AC input section 100, converts the rectifiedsignal into a dc voltage signal 311, provides the converted dc voltagesignal 311 to the dc-to-ac inverter 320. Preferably, the rectifier 310is an ac-to-dc diode rectifier.

The dc-to-dc converter 320 converts a voltage level of the dc voltagesignal 311 provided from the rectifier 310 into the dc voltage signal321, provides the dc voltage signal 321 to the second voltage convertingsection 400, controls a voltage level of a output dc voltage signal inresponse to a current detecting signal 601 provided from the currentdetecting section 600, and outputs the controlled dc voltage signal. Thedc-to-dc converter 320 can raise, lower the voltage level of theinputted dc voltage signal, or bypass the inputted dc voltage signal.

The dc-to-dc converter 320 outputs a dc voltage signal having a lowervoltage level than that of a dc voltage signal outputted from thedc-to-dc converter 320 in response to the current detecting signal 601when a larger current than a predetermined critical value is detected inthe load 500. The dc-to-dc converter 320 outputs a dc voltage signalhaving a higher voltage level than that of a dc voltage signal outputtedfrom the dc-to-dc converter 320 in response to the current detectingsignal 601 when a smaller current than a predetermined critical value isdetected in the load 500.

The second voltage converting section 400 a dc-to-ac inverter, raises orlower a voltage level of the dc voltage signal 321 provided from thedc-to-dc converter 320, converts the level shifted dc voltage signalinto an ac voltage signal 401, and provides the converted ac voltagesignal to the load 500.

The current detecting section 600 detects a current level of thecurrents flowing in the load 500, provides a current detecting signal601 corresponding to the detected current level to the dc-to-dcconverter 320 of first voltage converting section 300.

Hereinafter, a LCD having the power supply of FIG. 5 is disclosed.

FIG. 6 is a block diagram illustrating a LCD having the power supply inFIG. 5 according to one exemplary embodiment of the present invention.

Referring to FIG. 6, the LCD according to the present invention includesan AC input section 100, a first voltage -converting section 300, asecond voltage converting section 400, a fluorescent lamp 510, a currentdetecting section 600, a third voltage converting section 700 and a LCDmodule 800.

The AC input section 100 provides a general alternating current voltagehaving a current level between about 100 volts and about 240 volts tothe first voltage converting section 300. Generally, the AC inputsection 100 can provide the general alternating current voltage byputting an electric plug into a plug-socket.

The first voltage converting section 300 is an adaptor that includes arectifier 310 and a first dc-to-dc converter 320. The first voltageconverting section 300 rectifiers the general ac voltage signal 101,converts the rectified signal into a dc voltage signal 321, provides theconverted dc voltage signal 321 to the second voltage converting section400 and the third voltage converting section 700. Preferably, therectifier 310 can be an ac-to-dc diode rectifier.

The second voltage converting section 400 includes a dc-to-ac inverter,converts the dc voltage signal provided from the dc-to-dc converter 320of the first voltage converting section 300 into an ac voltage signal401, and provides the converted ac voltage signal 401 to the fluorescentlamp 510.

The fluorescent lamp emits a light to the LCD module 800 in response toan ac current signal provided from the second voltage converting section400.

The current detecting section 600 detects a current level of the lamptube current flowing in the fluorescent lamp 510, provides a currentdetecting signal 601 to the dc-to-dc converter 320 of first voltageconverting section 300.

The third voltage converting section 700 includes a dc-to-dc converter,converts the dc voltage provided from the first voltage convertingsection 300 into a plurality of dc voltage, and provides the convertedplurality of dc voltage to the LCD module 800. Preferably, the dc-to-dcconverter can be a flyback converter.

The LCD module 800 includes a common-electrode voltage generator 810, agamma voltage generator 820, a data driver, a gate driver and a LCDpanel 850, and displays an image in response to the dc voltage signalprovided from the third voltage converting section 700.

Specifically, the common-electrode voltage generator 810 generates acommon-electrode voltage (VCOM) based on the level shifted dc voltagefrom the third voltage converting section 700, and outputs thecommon-electrode voltage to the LCD panel 850.

The gamma voltage generator 820 generates a gamma voltage(VDD) based onthe level shifted dc voltage from the third voltage converting section700, and outputs the gamma voltage to the data driver 830.

The data driver 830 produces a gamma-corrected image signal fordisplaying an image based on the gamma voltage provided from the gammavoltage generator 820, and provides the gamma corrected image signal tothe LCD panel 850.

The gate driver 840 generates a scan signal based on a dc voltageprovided from the third voltage converting section 700, preferably agate-on/gate-off signal (Von/Voff), and outputs sequentially thegenerated scan signal to the LCD panel 850.

The LCD panel 850 includes a plurality of gate lines, a plurality ofdata lines, and a plurality of pixels. The gate lines transmit the scansignal from the gate driver 840. The data lines transmit a data voltagesignal provided from the data driver 830, are intersected with the gatelines, and are insulated from the gate lines. Each pixel is formed on aregion surrounded by the gate lines and data lines, is arranged in amatrix shape, and includes a TFT (Thin Film Transistor) that isconnected to gate line and data line.

When the gate-on signal is applied to the gate line and then the TFT isturned on, the data voltage (Vd) provided to the data line is applied toeach pixel electrode. An electric field, which is corresponding to thedifference voltage between the pixel voltage applied to the pixelelectrode and the VCOM applied from the common-electrode voltagegenerator 810, is applied to a liquid crystal capacitor, and a lighttransmits the liquid crystal with a transmittance corresponding to theapplied electric field, so that an image is displayed.

When the fluorescent lamp consumes a high voltage, in the conventionalinverter circuit raises again a voltage level of the input dc voltage bymeans of the buck converter, converts the raised dc voltage into an acvoltage, to thereby require 2 stages. However, according to the presentinvention, the high voltage that the fluorescent lamp requires can beprovided even though the buck converter is not used.

In addition, according to the present invention, the convenience andefficiency for driving the fluorescent lamp can be enhanced because theinverter circuit includes only a royer inverter block but not a buckconverter block, i.e. a dc-to-dc converter that is located at the frontstage of the royer inverter block.

FIG. 7 is a circuit diagram showing a specific circuit for implementingthe power supplier in FIG. 6.

Referring to FIG. 7, the first voltage converting section 300 includesan ac-to-dc diode rectifier 310 and a dc-to-dc converter 320. The firstvoltage converting section 300 rectifiers the general ac voltage signal,converts the rectified signal into a dc voltage signal, provides theconverted dc voltage signal to the second voltage converting section 400and the third voltage converting section 700.

Specifically, the ac-to-dc diode rectifier 310 includes a bridge diodehaving a first, second, third and fourth diodes (D1, D2, D3 and D4),rectifies the general ac voltage through the serially connected firstand second diode (D1, D2) and third and fourth diodes (D3, D4), andprovides the rectified dc voltage signal to the dc-to-dc converter 320.

The dc-to-dc converter 320 includes a inductor (L) of which a first endis connected to a output terminal of the ac-to-dc diode rectifier 310, afirst MOSFET (Q1) connected parallel to the bridge diode through theinductor (L), a fifth diode (D5) and a capacitor (C). The dc-to-dcconverter 320 smoothes the rectified voltage signal from the ac-to-dcdiode rectifier 310, raises a voltage level of the smoothen voltagesignal, and provides the level shifted dc voltage to the second voltageconverting section 400. Preferably, the switching device Q7 can be abipolar transistor, an emitter of Q7 is connected to a second end of thecapacitor (C1), a corrector of Q7 is connected to a primary coil of atransformer (T3), and a base of Q7 is connected a output terminal of thecurrent detecting section 600. The switching device Q7 controls theraising operation of the transformer (T3) in response to the currentdetecting signal 601.

The second voltage converting section 400 is a dc-to-ac inverter of aroyer type, converts a dc voltage signal provided from the dc-to-dcconverter 320 into an ac voltage signal, and provides the converted acvoltage signal to the fluorescent lamp 510.

Specifically, the dc voltage signal converted by the dc-to-dc converter320 is applied to bases of each transistor (Q7, Q9), which is an inputof the second voltage converting section 400, through parallel-connectedresistors (R1, R2). The primary coil of a transformer (T4) having acoil-tap is connected parallel with collectors of the transistors (Q8,Q9) of which emitter is connected to the ground, and is connectedparallel to a resonance capacitor (CR).

In addition, the dc voltage is applied to the coil-tap of the primarycoil of transformer (T4) through an inductor (L) including a choke coil(not shown) for converting the current provided to the second voltageconverting section 400 into a constant current.

The secondary coil of T4 has a winding number larger than the primarycoil of T4, raises a voltage level of the voltage signal applied to theprimary coil to a voltage signal having a higher voltage level, andprovides the raised voltage to the fluorescent lamp connected parallelto both ends of the secondary coil of T4. A positive and negative levelof the constant voltage can have the same magnitude, or the intervalbetween a maximum and minimum voltage level can be the same.

On the other hand, a first end of the primary coil of T5 is connected toa base of the transistor (Q8), a second end of the primary coil of T5 isconnected to a base of the transistor (Q9), and the voltage applied tothe primary coil of T5 is applied to the bases of transistors (Q8, Q9).

Hereinafter, the operation of the dc-to-ac inverter will be described.

First, when a dc voltage, which is a pulse signal, is applied to thedc-to-ac inverter, a current flows to the primary coil of T4 through theinductor (L). The dc voltage of a pulse shape is simultaneously appliedto the base of Q8 through the first resistor (R1), and applied to thebase of Q9 through the second resistor (R2). A reactance of the primarycoil of T4 and the resonance capacitor can generate a LC resonance. Araised voltage is induced at both ends of the secondary coil of T4, theraised voltage level being in proportion to a ratio N2/N1 (N1: windingnumber of the primary coil of T4, N2: winding number of the secondarycoil of T4). Simultaneously, a current flows at a primary coil of T5 ina reverse direction to a current flowing at a primary coil of T4.

Then, the voltage level of the second coil of T4 is raised in proportionto a winding ratio N1′/N1 (N1′: winding number of the primary coil ofT5, N1: winding number of the primary coil of T4), and a high voltagesignal with a frequency and phase synchronized with the secondary coilof T4 opposite to the primary coil of T4. The high voltage signal thathas a frequency and phase synchronized with the secondary of T4 canprevent a flicker phenomenon from generating in the fluorescent lamp510.

The fluorescent lamp 510 emits a light to the LCD module in response tothe ac voltage signal provided from the second voltage convertingsection 400. The fluorescent lamp 510 is a fluorescent lamp thatrequires an operation voltage having a higher voltage level—i.e. higherthan 2.5 Kv or higher than 3.0 Kv—than that of the operation voltagebetween 500 volts and 600 volts required by the CCFL. Namely, thefluorescent lamp 510 is a fluorescent lamp that can cover the entiresurface of the LCD panel when the fluorescent lamp is bended, forexample a EEFL or EIFL.

The current detecting section 600 detects a current level of thecurrents flowing through the fluorescent lamp 510, and provides thecurrent detecting signal 601 corresponding to the detected current levelto the dc-to-dc converter 320 of the first voltage converting section300.

Specifically, the current detecting section 600 includes a thirdresistor (R3), a seventh diode (D7) and an eighth diode (D8). A firstend of the third resistor is connected a second end of the fluorescentlamp 510, and a second end of the third resistor (R3) is connected tothe ground. A cathode of the diode (D7) is connected to the second endof the fluorescent lamp 510, and an anode of the diode (D7) is connectedto the ground. A cathode of the diode (D8) is connected to the dc-to-dcconverter 320, and an anode of the diode (D8) is connected to the secondend of the fluorescent lamp 510.

The current detecting section 600 detects the lamp tube currentoutputted through the second end of the fluorescent lamp, provides thedetected lamp tube current to the base of Q7, and requests to raise orlower the voltage level of the output dc voltage of the dc-to-dcconverter 320. The dc-to-dc converter 320 raises or lowers the voltagelevel of the output dc voltage based on the current detecting signal 601provided from the current detecting section 600, and the controlledoutput dc voltage is provided to the fluorescent lamp 510 through thedc-to-ac inverter 400.

A detail description about a third voltage converting section 700 is notrepeated because the third voltage converting section 700 is the same asthe dc-to-dc converter 242 of FIG. 4.

As mentioned above, according to the present invention, the firstvoltage converting section 300—i.e. an adaptor—converts the commercialac voltage inputted from the AC input section 100 into a dc voltagehaving a voltage level between about 150 volts and 250 volts, and into adc voltage having a voltage level about 12 volts. The converted dcvoltage having a voltage level between about 150 volts and 250 volts isused as a voltage source for driving a backlight, and the converted dcvoltage having a voltage level about 12 volts is used as a voltagesource for driving a LCD panel.

The royer inverter of the dc-to-ac inverter 400 raises the dc voltagehaving a voltage level between about 150 volts and 250 volts into ahigher ac voltage—i.e. about ac 3 Kv—that is a driving voltage of thefluorescent lamp consuming a high voltage. The current of thefluorescent lamp can be controlled by varying the output voltage—i.e.between about 150 volts and about 200 volts—of the first voltageconverting section 300.

According to the present invention, a relatively high dc voltage isconverted into a high ac voltage in the dc-to-ac inverter 400, and thecoil winding ratio—i.e. the ratio N1/N2 of the transformer (T4) locatedat a royer inverter of the dc-to-ac inverter 400—is several tens times,so that it does not require a transformer having a high winding number.

In addition, according to the present invention, it can solve anexcessive heating problem because a relatively high voltage, for examplebetween 150 volts and 250 volts, is applied to a power line of thedc-to-ac inverter 400 to reduce a current of the dc-to-ac inverter 400.

In addition, the dc-to-dc converter 320 of the first voltage convertingsection 300 directly receives a current feedback signal—i.e. currentdetecting signal 601—, and a buck converter can be removed while thedc-to-ac inverter is used, so that it can enhance power efficiency ofthe power supply according to the present invention.

As mentioned above, according to the present invention, a load can besupplied with a power without lowering the power efficiency even thoughthe load consuming power requires a high voltage, and the buck convertercan be removed from the inverter circuit that converts a dc voltage intoan ac voltage, so that a manufacturing cost can be reduced.

In addition, according to the present invention, a total cost formanufacturing the LCD monitor can be reduced by removing an external dcpower supply, a user can install and carry the LCD monitor conveniently,and working environment can be maintained clean.

In addition, according to the present invention, when manufacturing theLCD monitor used for a desktop PC, a number of voltage converting stepscan be decreased in comparison with the conventional voltage convertingsteps of the LCD monitor that uses the conventional power supply usedfor a notebook computer, to thereby enhance the efficiency of the powersupply.

In addition, according to the present invention, a transformer with asmall winding number can be substituted for the conventional transformerwith a large winding number by applying a high voltage to an invertercircuit.

In addition, according to the present invention, an inverter circuitwithout a transformer can be implemented, and the conventional dc-to-dcconverter (power module converter) can be used without any modificationof a circuit of the conventional dc-to-dc converter.

In addition, according to the present invention, a high dc voltage isconverted to a high ac voltage, and the converted high ac voltage isapplied to the dc-to-ac inverter, so that it is not required atransformer having a large winding number in the royer inverter of thedc-to-ac inverter.

Although the invention is described with reference to exemplaryembodiments, it is understood that the present invention should not belimited to these exemplary embodiments but various changes andmodifications can be made by one ordinary skilled in the art within thespirit and scope of the appended claims.

1. A power supplying apparatus, comprising: a first voltage convertingmeans for converting a first alternating current voltage into a firstdirect current voltage, and for changing a voltage level of the firstdirect current voltage into a second direct current voltage having ahigher voltage level than the voltage level of the first direct currentvoltage; a second voltage converting means for converting the seconddirect current voltage into a second alternating current voltage, andfor changing a voltage level of the second alternating current voltageinto a third alternating current voltage having a higher voltage levelthan the voltage level of the second alternating current voltage toprovide the third alternating current voltage to a first load; and acurrent detector for detecting a current flowing through the first load,and for providing a current detecting signal to the first voltageconverting means so that the first voltage converting means provides aconstant direct current output voltage, wherein the power supplyingapparatus includes an AC input section and a liquid crystal display(LCD) module section, wherein the first voltage converting means and thesecond voltage converting means are formed in the LCD module section,wherein the second voltage converting means comprises: a transformerincluding a primary coil and a secondary coil, the primary coil of thetransformer being connected to an output terminal of the first voltageconverting means, and the secondary coil of the transformer beingconnected the first load; a resonance capacitor, connected in parallelwith the primary coil, for forming an LC resonance circuit; a firsttransistor, a base of the first transistor being connected to the outputterminal of the first voltage converting means, a collector of the firsttransistor being connected to a first end of the resonance capacitor,and an emitter of the first transistor being connected to a ground, fordriving the transformer; a second transistor, a base of the secondtransistor being connected to the output terminal of the first voltageconverting means, a collector of the second transistor being connectedto a second end of the resonance capacitor, and an emitter of the secondtransistor being connected to the ground, for driving the transformer.2. A power supplying apparatus, comprising: a first voltage convertingmeans for converting a first alternating current voltage into a firstdirect current voltage, and for changing a voltage level of the firstdirect current voltage into a second direct current voltage having ahigher voltage level than the voltage level of the first direct currentvoltage; a second voltage converting means for converting the seconddirect current voltage into a second alternating current voltage, andfor changing a voltage level of the second alternating current voltageinto a third alternating current voltage having a higher voltage levelthan the voltage level of the second alternating current voltage toprovide the third alternating current voltage to a first load; and acurrent detector for detecting a current flowing through the first load,and for providing a current detecting signal to the first voltageconverting means so that the first voltage converting means provides aconstant direct current output voltage, wherein the second voltageconverting means comprises: a transformer including a primary coil and asecondary coil, the primary coil of the transformer being connected toan output terminal of the first voltage converting means, and thesecondary coil of the transformer being connected the first load; aresonance capacitor, connected in parallel with the primary coil, forforming an LC resonance circuit; a first transistor, a base of the firsttransistor being connected to the output terminal of the first voltageconverting means, a collector of the first transistor being connected toa first end of the resonance capacitor, and an emitter of the firsttransistor being connected to a ground, for driving the transformer; asecond transistor, a base of the second transistor being connected tothe output terminal of the first voltage converting means, a collectorof the second transistor being connected to a second end of theresonance capacitor, and an emitter of the second transistor beingconnected to the ground, for driving the transformer.
 3. The powersupplying apparatus of claim 2, wherein the first voltage convertingmeans comprises: a rectifying means for rectifying the first alternatingcurrent voltage into the first direct current voltage; and a dc-to-dcconverter for converting the first direct current voltage into thesecond direct current voltage to provide the second direct currentvoltage to the second voltage converting means, wherein said dc-to-dcconverter varies the voltage level of the second direct current voltagein response to the detected current signal.
 4. The power supplyingapparatus of claim 2, wherein the second voltage converting means is aroyer inverter, a push-pull Inverter, a half bridge Inverter or afull-bridge Inverter.
 5. The power supplying apparatus of claim 2,wherein the second voltage converting means further comprises a firstresistor, a first end of the first resistor being connected to the baseof the first transistor, and a second end of the first resistor beingconnected to the output terminal of the first voltage converting means.6. The power supplying apparatus of claim 2, wherein the second voltageconverting means further comprises a second resistor, a first end of thesecond resistor being connected to the base of the second transistor,and a second end of the second resistor being connected to the outputterminal of the first voltage converting means.
 7. The power supplyingapparatus of claim 2, wherein the first alternating current voltage is acommercial alternating current voltage, and the second direct currentvoltage has a voltage level between about 150 volts and about 200 volts.8. The power supplying apparatus of claim 2, wherein the first voltageconverting means further generates a third direct current voltage havinga voltage level lower than the voltage level of the first direct currentvoltage and provides the third direct current voltage to a second load,by receiving the first alternating current voltage.
 9. The powersupplying apparatus of claim 8, further comprising a third voltageconverting means for providing the third direct current voltage to thesecond load.